From their formation and throughout their development, primary tumors shed cells that circulate through the bloodstream of cancer patients. These circulating tumor cells (CTCs) potentially hold important clinical information that can be used for detection, characterization, accurate treatment and monitoring of cancer. While the presence of CTCs in the blood has been documented for over 100 years and various methods have been described for their detection. [M. Alumni-Fabroni and M. Sandri, Methods, 50 (2010) 289-297], these traditional methods have low sensitivity. Consequently, much of the research of the past decades has been focused on the development of reliable methods for CTC enrichment and identification, mainly trying overcome severe technical limitations.
In recent years, evidence supporting that the presence of CTCs in the blood can serve as a biomarker for potential disease and poor prognosis has continued to stimulate interest in the development of methodologies for detection and isolation of CTCs in blood samples from cancer patients. Another important attribute that has made the detection and isolation of CTCs attractive is the fact that despite of their heterogeneity, these cells may carry genetic information about the primary tumor that can be useful in guiding the treatment of a specific patient and providing an opportunity for individualize medicine. However, although many technologies have been recently developed recently for the detection and isolation of CTCs from peripheral blood samples of cancer patients, this task remains technically challenging.
This is mainly due to the fact that CTCs are rare and only occur at very low concentrations of one tumor cell per one billion blood cells. Typical methods for the identification and isolation of CTCs required extremely sensitive and specific analytical methods that generate very low yield and purity samples.
Circulating tumor cell (CTC) assays may powerfully improve the ability to monitor disease status, gauge prognosis, and guide treatment decisions for patients with cancer. However, CTC assays for many patients including those with brain tumors (such as Glioblastoma multiforme (GBM)) have not been possible due to the lack of surface expression of common biomarkers such as EpCAM to facilitate separation and subsequent detection. For other tumors such as non-small cell lung cancer (NSCLC), the ability to monitor treatment response may help reduce the lethality of lung cancer by overcoming limitations of imaging to monitor NSCLC disease state intra and post treatment, and avoid the need for a non-invasive means to assess NSCLC therapeutic effect and adjust the treatment plan accordingly.
The use of microfluidic devices for CTC detection and isolation has been described in the literature. In general, a microfluidic device handle relatively small cell numbers and sample volumes [e.g., from single cells to millions of cells, and from 10 to 200 microliters] making possible the detection and isolation of CTCs from a sample which may only contain few CTCs. Currently, some microfluidic systems have been described as useful for the detection of CTCs, including the CTC-Chip [S. Nagrath et “Isolating of rare circulating tumour cells in cancer patients by microchip technology”, Nature, 450: 123:5-1239 (20 Dec. 2007)], the herringbone-chip [S. L. Scott, et al, “Isolation of circulating tumor cells using a microvortex—generating herringbone chip, Proc Natl Acad Sci, vol. 107, no. 43, 18392-18397, e-pub Oct. 7, 2010, ahead of print Oct. 26, 2010] and the high-throughput microsampling unit (HTMSU) [A. Adams, et al, “Highly efficient circulating tumor cell isolation from whole blood and label-free enumeration using polymer-based microfluidics with an integrated conductivity sensor”, J. Am. Chem. Soc., 2008 Jul. 9; 130(27): 8633-41]. However, these systems present major technical limitations including the inability to capture non-epithelial cells (e.g. cells which do not express epithelial cell adhesion molecule (EpCAM). Capture efficiency and purity also merit improvement (M. Alunni-Fabroni and M. T. Sandri, “Circulating tumor cells in clinical practice: Methods of detection and possible characterization” Methods, 2010 Jan. 29; 50(4): 289-297).
Thus, there is still a need for a microfluidic device capable of capturing both epithelial and non-epithelial CTCs with high efficiency that yields a CTCs sample with high purity for accurately characterizing the biology of CTCs and to develop CTC analysis methodologies that can help guide diagnosis and treatment in a clinical setting. In addition, methods for qualitatively and/or quantitatively assessing CTC of a variety of tumor origins are still needed.